1. Field of the Invention
The present invention relates to a fuse reading circuit which reads data in a plurality of fuse circuits in which information is rewritten by trimming.
2. Description of the Related Art
A fuse circuit is known in the related art, which is used in a semiconductor integrated circuit (such as IC) for changing internal setting data in the semiconductor integrated circuit after the semiconductor integrated circuit is manufactured. More specifically, a fuse circuit is formed on a surface of an IC, and is trimmed using laser or a large current to cut the fuse and write information. In an IC, the trimming state of the fuse circuit can be read during startup of a system or the like, and the setting data can be changed based on a result of the reading process.
For example, JP 2006-72860 A discloses parallel connection of fuses to a resistor forming a part of a resistive voltage divider circuit, and cutting of the fuse with laser so that the resistance value of the divided voltage resistor circuit is adjusted.
Here, data of “0” or “1” can be written to the fuse circuit depending on whether or not the fuse circuit is cut, and, thus, in some cases, various digital data are set using the fuse circuit. For example, by providing two fuse circuits and a reading circuit, for each of the fuse circuits, which reads data by applying a voltage to one end of the fuse circuit and determining whether or not current flows through the fuse circuit, it is possible to read data of two bits.
When the number of bits of data which is set by the fuse circuit is small, the above-described structure is sufficient. However, when the number of bits is increased, not only the number of the fuse circuit is increased, but also the number of reading circuits is increased.
On the other hand, although a non-volatile memory is also widely in use for storage of a large amount of setting data, it is not efficient to prepare a non-volatile memory for storage of data having a size of few tens of bits.